code: def get_backend(backend_name, backends) -> Backend:
      if backend := backends.get(backend_name):
          return backend
      else:
          raise ValueError(
              f"Unsupported backend '{backend_name}' specified; ",
              f"please select one of {list(backends.keys())} instead.",
          )
  
file_path: audio/src/torchaudio/_backend/utils.py
imports: import os
  from functools import lru_cache
  from typing import BinaryIO, Dict, Optional, Tuple, Type, Union
  import torch
  from torchaudio._extension import lazy_import_sox_ext
  from torchaudio.io import CodecConfig
  from torio._extension import lazy_import_ffmpeg_ext
  from .None import soundfile_backend
  from .backend import Backend
  from .common import AudioMetaData
  from .ffmpeg import FFmpegBackend
  from .soundfile import SoundfileBackend
  from .sox import SoXBackend
label_desc: Use image node_id 2 for calling a global function with example usage: get_backend(backend_name, backends) and returns: backend